1. Field of the Invention
The present invention relates to a method of performing communication in a wireless communication system, and more particularly, to a ranging structure for supporting a legacy support mode and multiplexing method thereof. Although the present invention is suitable for a wide scope of applications, it is particularly suitable for using IEEE 802.16e ranging structure and IEEE 802.16m ranging structure together.
2. Discussion of the Related Art
A network entry procedure when a terminal is initiated in a broadband wireless access system will be described below.
(1) If a terminal is initially powered on, the terminal retrieves downlink channels and acquires uplink/downlink synchronization with a base station. At this time, the terminal receives a downlink-map (DL-MAP) message, an uplink-map (UL-MAP) message, a downlink channel descriptor (DCD) message, and an uplink channel descriptor (UCD) message to acquire uplink and downlink channel parameters.
(2) The terminal performs ranging with the base station to adjust uplink transmission parameters, and is allocated with basic management connection identifier (CID) and primary management CID from the base station.
(3) The terminal performs basic capability negotiation with the base station.
(4) The terminal performs its authentication procedure.
(5) The terminal is subscribed to the base station, and the terminal managed by IP is allocated with secondary management CID from the base station.
(6) The terminal sets IP connection.
(7) The terminal sets the current date and time.
(8) The terminal downloads its configuration file from a TFTP server.
(9) The terminal sets connection of a service which is previously prepared.
FIG. 1 is a flow chart illustrating the aforementioned procedure.
A physical layer of a broadband wireless access system is divided into a single carrier scheme and a multiple carrier scheme (OFDM/OFDMA). The multiple carrier scheme uses OFDM, and introduces an OFDMA (Orthogonal Frequency Division Multiple Access) scheme as an access scheme that can allocate resources in a unit of sub-channel by grouping a part of carriers.
A physical layer of the OFDMA scheme divides active carriers into a plurality of groups and transmits the respective groups to different receiving sides. In this way, a group of carriers transmitted to one receiving side is referred to as a sub-channel. Carriers constituting each sub-channel may be located to be adjacent to each other or may be spaced apart from each other at constant intervals. Such a multiple access in a unit of sub-channel may increase complexity but is advantageous in that frequency diversity gain and gain subject to concentration of power can be obtained, and forward power control can efficiently be performed.
A slot allocated to each user is defined by a data region of a two-dimensional time-frequency sphere, and is a set of continuous sub-channels allocated by burst. One data region in the OFDMA scheme is a rectangular form sectioned by time and sub-channel coordinates. Such a data region can be allocated to an uplink for a specific user, or a base station can transmit the data region to a specific user in a downlink. In order to define such a data region on the two-dimensional sphere, the number of OFDM symbols in the time domain and the number of continuous sub-channels starting from a point having an offset from a reference point in the frequency domain should be given.
FIG. 2 illustrates a frame structure of a physical layer of an OFDMA scheme in a broadband wireless access system. A downlink sub-frame starts with a preamble used for synchronization and equalization in a physical layer, and a structure of the entire frame is defined through a broadcast type downlink-map (DL-MAP) message and uplink-map (UL-MAP) message which define location and usage of burst allocated to a downlink and an uplink.
The downlink map (DL-MAP) message defines usage allocated per burst for a downlink interval in a burst mode physical layer while the uplink map (UL-MAP) message defines usage of the burst allocated for an uplink interval. An information element constituting the DL-MAP message divides a downlink traffic interval in a user terminal through downlink interval usage code (DIUC) and location information of burst (sub-channel offset, symbol offset, the number of sub-channels, and the number of symbols). Meanwhile, usage of an information element constituting the UL-MAP message is defined by uplink interval usage code (UIUC) per connection ID (CID), and location of a corresponding interval is defined by ‘duration.’ Usage per interval is defined in accordance with the UIUC value used in the UL-MAP, and each interval starts from a point away from a start point of a previous information element (IE) by ‘duration’ defined in the UL-MAP information element (IE).
The main standard defined by the IEEE 802.16 task group includes IEEE 802.16-2004 called fixed WiMAX and IEEE 802.16e-2005 called mobile WiMAX. The IEEE 802.16e-2005 has been finally approved from the IEEE on December of 2005. The standard based on mobile WiMAX of a current version includes IEEE 802.16-2004, IEEE 802.16e-2005 (this document includes Corrigenda of IEEE 802.16-2004), and IEEE 802.16-2004/Corrigenda2/D4 (based on August of 2007). Subsequently, standardization of IEEE 802.16m for mobile WiMAX of next version is in progress by TGm within the IEEE 802.16 task group.